The present invention relates to a backside covering material used for a rear surface protection member of a solar cell module and a solar cell module using said material. Particularly, it relates to the backside covering material for a solar cell module having excellent moisture resistance and durability and insulating very well to prevent leak current, and to a durable and high-performance solar cell module using the material as the rear surface protection member.
A solar cell module has been paid attention as a device directly converting solar energy into electric energy from the aspects of effective use of natural resources and ecology, and various solar cell modules have been developed.
As shown in FIG. 3, in a solar cell module, solar cells 14 (photovoltaic element made of silicon etc.) are sealed by ethylene-vinyl acetate copolymer (EVA) films 13A, 13B in between a transparent front surface (light receiving face) protection member 11 and a rear surface protection member (backside covering material) 12.
A solar cell module 10 is produced by the following procedures. First, a front surface protection member 11 made of glass or the like, EVA film 13A for sealant, silicon photovoltaic element 14, EVA film 13B for sealant, and a backside covering material 12 are stacked up in this sequence. Then, EVA is melted by heat and cross-linked to unify the whole solar cell module.
A backside covering material is desired to be light and thin to make a solar cell module light and thin. The backside covering material is also desired to have durability in a long term since a solar cell module is usually installed outside. Further, the backside covering material needs to have high moisture resistance to prevent permeation of moisture and water causing rusting in underlying parts such as photovoltaic element, wire, and electrodes.
The conventional backside covering material is a laminated film comprising metal foil such as aluminum foil and galvanized iron foil as a moisture preventing layer put between two resin film layers.
However, there are several disadvantages associated with the conventional backside covering material using metal foil. First, a solar cell module using the conventional material sometimes has leak current. Second, projections of underlying parts such as a photovoltaic element and a wire may penetrate through a resin film to cause a short-circuit with metal foil. Third, a laminated resin film without including metal foil cannot give enough moisture resistance.
An object of this invention is to provide a backside covering material for a rear surface protection member of a solar cell module which doesn""t have any disadvantages mentioned above, is light and thin, has improved moisture resistance and durability, and also is a good insulator. Another object of this invention is to provide a solar cell module with high durability and performance using the backside covering material for a rear surface protection member.
The backside covering material for a solar cell module in this invention includes a moisture resistant film disposed between two films having heat resistance and weather resistance, wherein the moisture resistant film has a deposited layer of inorganic oxide on a surface of a base film.
The backside covering material of this invention is light and thin. The moisture resistant film having the base film and the deposited layer of inorganic oxide on the surface of the base film is highly moisture resistant and is an excellent insulator so that a short-circuit and leak current associated with underlying parts such as a photovoltaic element and a wire of a solar cell module is prevented.
Inorganic oxide used for the deposited layer of the moisture resistant film is preferably silicon oxide, most preferably SiOx, where x is in a range of 1.7-1.9. The thickness of the deposited layer is preferably in a range of 100-500 xc3x85.
An anchor coat layer may be formed between the base film and the deposited layer of inorganic oxide. The anchor coat layer ensures the prevention of moisture permeating through the backside covering material of a solar cell module for a long time. The anchor coat layer may be of acrylic urethane resin.
The backside covering material of a solar cell module of this invention may also have an adhesive layer on one surface thereof.
The backside covering material of a solar cell module of this invention may have moisture permeability not higher than 1.0 g/m2/day.
In this invention, it is preferred to use hydrogenated polybutadiene-denatured urethane adhesive to bond the film having heat resistance and weather resistance and the moisture resistant film.
A solar cell module of this invention includes at least one solar cell, a front surface protection member and a rear surface protection member. The solar cell(s) is disposed between the front surface protection member and the rear surface protection member, and the solar cell(s) is sealed by the protection members. The rear surface protection member is made of the backside covering material of this invention.